Date of Award

Fall 2003

Project Type

Dissertation

Program or Major

Plant Biology

Degree Name

Doctor of Philosophy

First Advisor

Thomas D Lee

Abstract

The decline of Atlantic white-cedar (Chamaecyparis thyoides) throughout its range has motivated researchers to investigate cedar seedling recruitment. In this study, conducted at Brown Mill Pond in Rye, New Hampshire, the distribution pattern of cedar seedlings was studied in order to identify which, if any, biological or physical factors observed at a microtopographic scale were associated with seedling presence. On a landscape scale, five previously identified cedar communities were measured for differences in water table level and soil moisture in order to determine associations between stand dynamics and hydrology.

A field survey showed that cedar seedlings were (1) absent from hummocks with tussock sedge substrate and present on hummocks with moss or litter substrate, (2) most frequent 10--25 cm above the July water table, at "intermediate" elevations, and were less common between 25--60 cm on these hummocks.

Several multi-factor field experiments tested whether factors identified in the survey, specifically substrate type and elevation relative to the water table, influenced cedar seedling emergence, growth, or survival. In one set of experiments, seeds and seedlings were transplanted to hummocks having different substrates. In contrast to results of the survey, these experiments indicated substrate type did not influence seedling emergence, growth, or survival. The lack of cedar seedlings on tussock sedge hummocks may be explained by hummock area rather than substrate quality, as tussock sedge hummocks were generally smaller than the moss-litter hummocks. In another set of experiments, seeds and seedlings were transplanted to different hummock elevations where some received supplemental water. The experiments showed that elevation relative to the water table influenced cedar seedling emergence and performance, and that moisture was a primary limiting factor in natural regeneration at this site.

Differences in water table level and soil moisture were associated with differences in species composition and stand structure among the five cedar communities. In the wettest community continuous establishment of cedar was evident, while in the driest community red spruce (Picea rubens) and eastern hemlock (Tsuga canadensis) dominated the understory and were expected to replace cedar over successional time.

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